The present invention is directed to integrated circuits. More particularly, the invention provides systems and methods for system protections. Merely by way of example, the invention has been applied to over-temperature protection and over-voltage protection of power conversion systems. But it would be recognized that the invention has a much broader range of applicability.
Power conversion systems are often used in many electronic devices to provide power for the electronic devices to operate properly. To protect the electronic devices from being damaged under certain circumstances, many power conversion systems usually include certain protection mechanisms, such as over-temperature protection (OTP) and over-voltage protection (OVP). Oftentimes, a controller chip of a power conversion system uses two different terminals (e.g., pins) for OTP and OVP respectively. In certain controller chips, a terminal is used for OTP, and another terminal for current sensing (e.g., a CS terminal) is used for OVP. But the related OVP detection circuit may disturb the current sensing mechanism. In some controller chips, a single terminal (e.g., a pin) may be selected to perform OTP or selected to perform OVP, but cannot be selected to perform both OTP and OVP.
FIG. 1 is a simplified conventional diagram for over-temperature protection of a power conversion system. The power conversion system 10 includes a controller 12, a primary winding 14, a secondary winding 16, an auxiliary winding 18, a switch 20, resistors 22 and 24, diodes 26 and 28, capacitors 30 and 32, and a feedback component 34. The controller 12 includes terminals (e.g., pins) 36, 38, 40, 42, 44 and 46. For example, the switch 20 includes a field effect transistor. In another example, the switch 20 includes a bipolar junction transistor. In yet another example, the switch 20 includes an insulated-gate bipolar transistor.
As shown in FIG. 1, the resistor 22 is coupled to the terminal 36 (e.g., terminal OTP) for OTP detection. For example, the resistor 22 is a thermal resistor (e.g., a thermistor) that changes its resistance with temperature. As an example, the resistor 22 has a negative temperature coefficient, i.e., the resistance of the resistor 22 decreases with increasing temperatures. When the temperature of the power conversion system 10 is higher than a threshold temperature (e.g., T0), the resistance of the resistor 22 becomes smaller than a threshold resistance (e.g., R0), in some embodiments. For example, if a current 48 (e.g., IOTP) flowing through the resistor 22 does not change in magnitude with temperature, a voltage drop across the resistor 22 is determined as follows:VRT=IOTP×R0  (Equation 1)If the voltage drop across the resistor 22 is smaller in magnitude than a predetermined reference voltage, it is determined that the temperature of the power conversion system 10 is too high. For example, if the voltage drop across the resistor 22 remains smaller in magnitude than the predetermined reference voltage during a predetermined time period (e.g., N clock cycles), the OTP mechanism is triggered and the controller 12 changes a drive signal 50 to open (e.g., turn off) the switch 20 in order to power off the power conversion system 10. But the controller 12 cannot perform OTP detection and OVP detection using a single terminal (e.g., terminal 36).
The controller 12 includes no additional terminals other than the six terminals (e.g., the six pins) 36, 38, 40, 42, 44, and 46. For example, the terminal 38 (e.g., terminal VCC) is used to receive a supply voltage for the controller 12, and the terminal 44 (e.g., terminal CS) is used to receive a current-sensing signal associated with a primary current flowing through the primary winding 14. In another example, the terminal 42 (e.g., terminal GND) is biased at a ground voltage, and the terminal 40 (e.g., terminal GATE) is used to output the drive signal to open (e.g., turn off) and/or close (e.g., turn on) the switch 20. Alternatively, the controller 12 includes one or more additional terminals (e.g., one or more additional pins) other than the six terminals (e.g., the six pins) 36, 38, 40, 42, 44, and 46.
Hence it is highly desirable to improve the technique for achieving OTP and OVP in power conversion systems.